Exhaust gas recirculation (EGR) systems may be used in internal combustion engines to reduce NOx emissions. In the combustion chambers, the recirculated exhaust gas acts as an inert gas, thus lowering the flame and in-cylinder gas temperature and decreasing the formation of NOx. Further, EGR systems may include coolers to cool the exhaust gas before it is introduced into an intake manifold of a diesel engine.
EGR valves may be required to meter the flow of recirculated exhaust gas to the intake manifold. EGR valves have been disposed on the “cold side” (downstream) of the EGR cooler for improved packaging and temperature durability issues. However, in these configurations, EGR valves may be exposed to condensed exhaust constituents such as hydrocarbons and acidic compounds which create contamination and corrosion. The EGR valve housing may also be sensitive to corrosion from acidic condensates. While a high temperature is beneficial in preventing the condensation of gas and corrosion, the electronic components in the EGR valve may be degraded at the high temperature. Thus, it may be desirable for less heat to be transferred to the electronic components of the EGR valve in some situations.
One approach to solve the above problem is described in the U.S. Pat. No. 6,213,105. In particular, the EGR valve is mounted on the supply side of the exhaust cooler (the side at which the hot exhaust enters) so that there is a relatively small amount of residue from the exhaust adhering to the valve and its valve elements. The adjustment element including electronic components is isolated thermally from the valve and disposed outside the EGR cooler, and accordingly is subject to relatively low heat stress.
However, the inventor herein has recognized disadvantages with such an EGR system. For example, the electronic components are disposed at a hot side of an engine compartment and may still be subject to undesirable heat. Further, this configuration may limit the packaging and the types of EGR valves that can be used in the EGR system because of the requirement of isolation between a valve and its electronic components. Furthermore, the “pick-up” of EGR gases is typically from the rear of the engine, either from the exhaust manifold or turbocharger plumbing. This means that an EGR valve located on the hot side of the EGR cooler is driven to the rear of the engine compartment, close to other hot components and generally in a more restricted package environment due to cowl overhangs and other neighboring components. Under hood temperatures in this area of the engine compartment can exceed the temperature limits of the EGR valve's electrical components even if the electrical components are effectively decoupled from the hot valve body via cooling.